The portable electronic device such as a laptop computer, a personal digital assistant (PDA), a portable digital video disk (DVD), a camcorder, a digital camera, a cellular phone and the like is provided with a battery during traveling. To charge the battery and use the equipment, DC power with a suitable voltage should be applied to the battery and the equipment through a connector having a proper shape. However, rated voltages of the portable electronic devices differ form each other according to the kinds of the device as well as the manufacturer, and shapes of input section to which DC power is supplied are different form each other according to the kinds of devices. Accordingly, the user having the various kinds of portable electronic devices should be carrying several power supply devices which are generally called as “adapter” and should purchase several adapters according to the electronic device, and so the user suffers economical loss.
As an attempt to solve the above problems, the universal power supply apparatus is provided. The universal power supply apparatus is a power supply apparatus which is applicable to various kinds of portable electronic devices with one main unit.
In such universal power supply apparatus, a detachable tip or cable which is applied in the different manners according to a shape of power input terminal of the device should be provided and a method for setting a voltage suited for the electronic device to be used should be provided.
In the conventional universal power supply apparatus general well known, a voltage of the device to be used is set in the main unit by using dip switch, rotary switch or a resistance substance with a special shape as disclosed in U.S. Pat. No. 5,347,211 and a tip or cable separated from the main unit and corresponding to a shape of power input terminal of the electronic device to be used is provided. However, the universal power supply apparatus has a drawback that the user finds the tip or cable which can be used for the portable electronic device and set a voltage suitable for the electronic device in the main unit so that it is difficult to use the universal power supply apparatus for the consumer with no electronic knowledge or skills.
In order to overcome the above drawbacks, a method for providing a special unit being capable of changing a voltage at the tip or cable in the entire cable is disclosed in U.S. Pat. No. 5,510,691, U.S. Pat. No. 6,604,177, U.S. Pat. No. 6,091,611 and the like. The special unit used in the above method comprises at least one of electronic elements such as resistor, condenser, diode and the like, this unit is generally referred to as “a daughter electronic circuit”. However, when such electronic element is mounted to the tip, it is difficult to manufacture and inspect the tip, and a manufacturing cost of the tip is increased. In particular, there is a drawback that it is most difficult to minimize the tip.